One-time programmable (OTP) memories typically include a set of OTP memory cells. An OTP memory with cells based on fuses can be programmed by blowing selected ones of the set of fuses. One or more sense circuits are then able to read the combination of blown and intact fuses in the OTP memory in order to store a desirable data pattern. One application of a fuse-based OTP memory is to use the stored data pattern to select the optional functionality of an integrated circuit. In this way the same integrated circuit die can be used in a variety of applications. One example of an industry that makes use of OTP memories is the automotive industry.
Silicided polysilicon resistors are commonly used as fuses in submicron integrated semiconductor technologies. Fuses such as these are typically programmed by applying a fixed voltage across the fuse for a predefined period of time. The fixed applied voltage drives programming current through the fuse causing silicide migration within the fuse and resulting in an increased resistance relative to initial resistance. Because the characteristics of each fuse in the memory are different due to normal process variation, and because each memory cell is connected to external circuitry differently due to necessity, they respond differently to the programming stimuli. Therefore, the programming with fixed stimuli results in a relatively wide distribution of resistance after programming. In fact, if the programming time is too long, the programming of some OTP memory cells can fail causing the fuse to be erroneously read as intact. If the programming time is too short, the programming of some fuses can fail causing the same erroneous result. Thus, OTP memories often require multiple redundant OTP memory cells because incorrect programming of OTP memory cells can occur too frequently adding unnecessary cost to the device. More importantly, programming in this manner can lead to undesirable reliability issues. It is difficult to determine an acceptable, predefined programming time that accounts for all reasonable variation of process, voltage, and temperature.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items.